Method of preparing wood impregnant



Patented July 28, 1942 UNHTED STATES METHOD OF PREPARING WOOD IIVIPREGNANT Jacquelin E. Harvey, Jr., Atlanta, Ga., assignor of one-half to Southern Wood Preserving Company, East Point, Ga., a corporation of Georgia 1 Claim.

The present process relates to the elimination, at least partial, of the toxicity blanketing efiect in wood preserving impregnants.

In the preparation of wood preserving impregnants from oils of aromatic content, it has long been a desideratum in the art to provide a preserving impregnant of maximum toxic properties without sacrificing permanency. However, research has disclosed that maximum toxic properties and good permanency of Wood preserving impregnant are not always compatible. To secure a high toxic efiiciency of a wood preserving impregnant, the permanency of the impregnant must, to a certain degree, be sacrificed. The converse is true.

As an example of a wood preservin impregnant of high toxic properties, but of relatively low permanency, may be mentioned a coal tar creosote, identification No. 7838, having 47.7% distilling above 270 C. and a killing concentration of 0.075%. By killing concentration is meant the percentage of the wood preserving impregnant required to kill wood destroying fungi and is fully described on page 2 under the caption Method of conducting the test, in Technical Bulletin No. 346, March, 1933, U. S. Department of Agriculture.

In the tabular data shown below are listed several woo-d preserving impregnants and the indicated relationship between their residue above 270 C. and their respective killing concentrations.

As indicated by the tabular data shown above, the impregnant having the highest residue above 270 C. is the least toxic and those having the lowest residue above 270 C. are the most toxic. However, those having the least residue above 270 C. are the least permanent in the Wood treated therewith. Many and divergent theories have been advance-d for the decrease in toxicity as the residue in the impregnant above 270 C. increases.

The present process is concerned with a novel manner of eliminating, at least to a degree, the apparent toxicity blanketing efiect of the residue above 270 C., which statement is meant to include the elimination of the apparent toxicity blanketing effect in the entire residue above 270 C. or any fractional part thereof, for it has been shown that beneficial toxic results are accomplished by eliminating or lowering the toxicity blanketing effect in only a portion of the residue above 270 C., as for instance the residue above 355 C.

There are, perhaps, many reasons attaching to the decrease of toxicity as the residue above 270 C. increases, which, however, is of no concern to the development of the data at hand.

It is now discovered that, perhaps among other things, the character of the residue above 270 C. influences the reduction of toxicity. In wood preserving impregnants of the oil type, as for instance impregnants of the tar-derived type, the fractions above 270 C. contain in varying percentages oxygen-containing compounds, the presence of which tends to blanket the toxicity of the impregnant in question.

Research has disclosed that the toxicity blanketing effect of the residue above 270 C. may be eliminated, at least to a degree, by the decomposition or partial decomposition of the oxygenated compounds contained in said residue.

The following examples will serve to illustrate modes of practicing the process, but are not to be construed as limitations inasmuch a those skilled in the art will readily recognize that the present process is possible of many variations.

Example 1.-A coal tar creosote having an oxygen containing residue of 47.7% above 270 C. and a killing concentration of 0.075% is stripped to remove the residue above 270 C. The residue is treated with hydrogen at 400 C. and 275 atmospheres pressure for one hour, the while including the presence of a catalyst selected from the group consisting of halogens, halids and derivatives thereof. By the inclusion of said catalyst oxygenated compounds are decomposed. The treated residue of lowered oxygen content is blended with the originally stripped low boiling material to provide an overall toxic material having a killing concentration of less than 0.075%.

EmampZe 2.-A coal tar having an oxygen containing residue of above 270 C. and a killing concentration of 2.5% is stripped to remove the residue above 270 C. The residue is treated with hydrogen at 410 C. and 300 atmospheres pressure for one and one-half hours, with the inclusion of three tenths percent iodine based on the weight of the residue. By the aid of the inclusion of said iodine, oxygenated compounds are decomposed at least partially. The treated residue of lowered oxygen content is then commingled with the originally stripped w boiling material to provide an overall toxic material having a killing concentration of less than 2.5%.

Example 3.-A coal tar is distilled to substantial dryness to provide a creosote having an oxygen containing residue of 73% above 270 C'. and a killing concentration of 0.35%. As the creosote is being recovered from the coal tar it is cut into two portions, the out being made at substantially 345 C. The residue above 345 C. is subjected to the action of hydrogen at 415 C. and a pressure of 200 atmospheres for a period of one hour, the while including a catalyst adapted to influence the decomposition of oxygen containing compounds, said catalyst being selected from the group consisting of halogens, halids and derivatives thereof. The treated residue of lowered oxygen content is then commingled with the low boiling portion of the creosote previously cut to provide an overall toxic material having a killing concentration of less than 0.035%.

Example 4.-A high residue creosote having substantially 75% residue above 270 C. and a killing concentration of substantially 0.3% is stripped up to: 355 C. to provide a residue characterized by oxygen containing compounds that blanket toxicity in the parent material. The oxygen containing residue is treated with hydrogen in the presence of a catalyst selected from the group consisting of halogens, halids and derivatives thereof; time of treatment, two and one quarter hours and pressure 300 atmospheres. The treated residue of lowered oxygen content is distilled to an upper limit to provide a residue having an initial boiling point similar to the high boiling point of the distillate previously recovered from the high residue creosote starting material. The distillate first recovered and the residue last named are commingled to provide an overall toxic material having a killing concentration of less than 0.3

Viewed broadly, the present invention provides a process for decomposing at least a portion of the oxygen containing compounds contained in said residue above 270 C. of toxic materials whose toxic efficiency is blanketed by the presence of'said oxygenated compounds.

Pressures and temperatures of in excess of atmospheres and 300 C., respectively, are preferred. However lower pressures and temperatures may be used but the time element will be extended.

Minor changes may be made within the scope of the appended claim without departing from the spirit of the invention.

I claim:

In the diminution of toxicity-blanketing effect in a high temperature coal tar creosote due to oxygenated compounds contained in the residual material boiling above 270 0., the process which comprises: stripping said creosote at a temperature not below 270 0. to provide a distillate and a residual having oxygen-containing fractions; subjecting said residual to a single action of hydrogen catalyzed by a catalyst selected from the group consisting of halogens, halids and derivatives thereof, said catalyst adapted to influence the elimination of oxygen from said oxygen-containing residual; continuing the treatment for such a length of time and with pressure and temperature so chosen as to provide at least partial elimination of oxygen from said residual; distilling the treated residual to provide a newly formed residual having an initial boiling point similar to the high boiling point of the distillate first "named; and commingling the residue last named with the distillate first named whereby to provide a toxic material having a smaller killing concentration than the parent material.

JACQUELIN El. HARVEY, JR. 

